the surface of the earth and in the
atmosphere as a result of cosmic
radiation and the presence of radio-
isotopes in the earth’s rocks, soil,
and atmosphere. The radioisotopes
are either natural or the result of nu-
clear fallout or waste gas from power
stations. Background counts must be
taken into account when measuring
the radiation produced by a speciÜed
source.
back titration A technique in *vol-
umetric analysis in which a known
excess amount of a reagent is added
to the solution to be estimated. The
unreacted amount of the added
reagent is then determined by titra-
tion, allowing the amount of sub-
stance in the original test solution to
be calculated.
bacteriocidal Capable of killing
bacteria. Common bacteriocides are
some antibiotics, antiseptics, and dis-
infectants.
bacteriorhodopsin A membrane-
bound protein of the halophilic (salt-
resistant) bacterium Halobacterium
halobium. When activated by light, it
pumps protons out of the cell; this
creates a concentration gradient,
which enables ATP to be synthesized.
Bacteriorhodopsin is composed of
seven α-helix segments, which span
the membrane and are joined to-
gether by short amino-acid chains. It
contains the prosthetic group retinal,
which is also found in the pigment
rhodopsin in the rod cells of verte-
brates.
Baeyer, Adolf von (1835–1917)
German organic chemist noted for
his work on organic synthesis. He
synthesized and determined the
structure of indigo and also synthe-
sized some of theÜrst barbiturates.
In his work on carbon rings he for-
mulated his strain theory. Bayer was
awarded the 1905 Nobel Prize for
chemistry.Baeyer strainSee angle strain.Baeyer testA test for unsaturated
compounds in which potassium per-
manganate is used. Alkenes, for ex-
ample, are oxidised to glycols, and
the permanganate loses its colour:
3R 2 C=CR 2 + 2KMnO 4 + 4H 2 O →
2MnO 2 + 2KOH + 3R 2 COHR 2 COHBaeyer–Villiger reaction A re-
arrangement reaction, sometimes
known as the Dakin reaction, com-
monly used in organic synthesis in
which a ketone reacts with a peroxy
acid to form an ester. For example,
R–CO–R →R–CO–O–R
The reaction is equivalent to the in-
sertion of an oxygen atom next to
the ketone’s carbonyl (>C=O) group.
Meta-chloroperbenzoic acid (m-CPBA;
ClC 6 H 4 .CO.O.OH) and triÛuoro-
perethanoic acid (CF 3 .CO.O.OH) are
typical peroxy acids employed in the
reaction. It was discovered by Adolf
von *Baeyer and the German
chemist V. Villiger in 1899.BakeliteA trade name for certain
*phenol–formaldehyde resins,Ürst
introduced in 1909 by the Belgian–
US chemist Leo Hendrik Baekeland
(1863–1944).baking powderA mixture of pow-
dered compounds added to dough or
cake mixture to make it rise in cook-
ing. It is used as a substitute for yeast
in bread-making. Baking powders
consist of a source of carbon dioxide,
such as sodium hydrogencarbonate
or ammonium hydrogencarbonate,
and an acidic substance such as cal-
cium hydrogenphosphate, potassium
hydrogentartrate (cream of tartar), or
sodium hydrogenphosphate. In the
hot wet mixture, the acid releases
bubbles of carbon dioxide gas from55 baking powder
b